(1) Technical Field
This invention relates to electronic circuits, and more particularly to calibration and testing architectures for radio frequency integrated circuits.
(2) Background
Radio frequency (RF) integrated circuits (ICs) may include a number of different RF signal paths and involve multiple inputs and outputs, such as is the case with multi-antenna/multi-transceiver RF ICs. Such RF IC's may be used, for example, in communication or radar systems that utilize beamforming techniques for directional signal transmission and/or reception. Beamforming combines transmit/receive elements in a phased array in such a way that signals at particular angles experience constructive interference while other signals at other angles experience destructive interference. Beamforming can be used at both the transmitting and receiving ends of a communication system in order to achieve spatial selectivity. Another advantage of beamforming is that the directional nature of the link means that less power needs to be transmitted to achieve a good signal to noise ratio at the receiver because all of the signal energy is directed at the receiver rather than being dispersed omni-directionally.
The quality of beamforming depends on how accurately multiple transceivers on an IC track each other with respect to at least phase and attenuation. It is possible to adjust the settings of different transceiver phase shifters circuits and attenuators circuits if the performance of each transceiver is known in advance. Measured differences between transmitted and received signals may be used to adjust (calibrate) the phase and/or attenuation state of one transceiver with respect to the other transceiver. However, accurate calibration measurements of such performance are difficult to obtain in an assembled final system where all measurements need to be done “over the air”, meaning actually transmitting a signal (which may be varied over a band of frequencies) from one transceiver through an antenna and receiving that signal in a different transceiver through an antenna. Such measurements require relatively elaborate testing equipment capable of dealing with high frequency RF signals (e.g., up to 30 GHz or more) and may be heavily influenced by environmental factors in the test set-up that alter, shield, attenuate, distort, or otherwise affect the transmitted and received signals. Furthermore, the accuracy or performance of a transceiver will vary over the possible bandwidth of the system, and therefore adjustments may need to be made dynamically depending on the instantaneous frequency of operation.
Accordingly, there is a need to be able to calibrate RF ICs used in multi-transceiver RF systems more accurately, preferably with a simpler testing environment. The present invention meets this need and more.